I’m with Gott n Wynne too! Recently my heated screen failed, total PITA when raining but frankly I don’t think it worked from new as rarely used and only discovered when out of warranty.
Screen replaced at the Factory, £1200 less £120 excess IIRC.

1969 4/4
1995 plus 8
1996 Plus 4 4seater
2002 Aero S1
2013 M3W
2014 Plus 8